An integrated circuit formed in a semiconductor wafer is generally subjected to an electrical test (i.e., to check the quality of the integrated circuit) as to whether or not it has predetermined electrical characteristics). Such a test may be performed for all integrated circuits in one wafer at one time or at separate times by using an electrical connecting apparatus such as a probe card which electrically connects an electrode of the integrated circuit with an electric circuit of a test apparatus.
The connecting apparatus to be used for such a test may include a wiring board having a plurality of connecting portions to be electrically connected to the electric circuit of the test apparatus, a probe base plate having a plurality of internal wires on the underside of the wiring board and electrically connected to the connecting portion, and a plurality of contacts (i.e., probes) attached to the underside of the probe base plate and electrically connected to the internal wires. This connecting apparatus may be mounted on the test apparatus or on the outer peripheral portion of a reinforcing member attached to the upside of the wiring board.
In the above-mentioned connecting apparatus, the tip of each contact is pressed against an electrode of the integrated circuit to be elastically deformed and is able to slide on the electrode of the integrated circuit. Thus, an oxide film formed on the surface of the electrode of the integrated circuit may be scraped off by the tip, so that the contact and the electrode of the integrated circuit are brought into good electrical contact. In this state, electrical signals for the test between the contact and the integrated circuit are transmitted.
With the recent tendency of larger-sized wafers, those having a diameter larger than 300 mm are being manufactured. For testing such a larger-sized wafer, demand for a larger-sized connecting apparatus for a larger number of integrated circuits to be tested simultaneously at one time is growing. Thus, probe base plates tend to be more and more larger-sized, with more contacts attached to a probe base plate, thereby enabling the test more integrated circuits simultaneously.
Nowadays, wafers having a diameter larger than 300 mm are manufactured, and the diameters of a wiring board and a probe base plate of an electrical connecting apparatus to be used for testing integrated circuits of such a wafer may be over 400 mm.
In view of the above, for the purpose of stabilizing a state of electrical connection (i.e., conductivity) between a contact and an electrode of an integrated circuit, there is proposed a technology to flatten the probe base plate to make uniform the heights of the tips of the contacts relative to the integrated circuit, a technology to forcibly prevent the probe base plate from bending, which may occur when the tips of the contacts are pressed against the electrodes of the integrated circuits, and the like. Examples of these technologies are shown generally in JP Patent Appln. Public Disclosure No. 2006-210473 and JP Patent Appln. Public Disclosure No. 2007-500945, which are incorporated by reference.
However, because of the tendency of a probe base plate to become larger and to include an increased number of contacts attached to the probe base plate, it happens that, the higher the number of contacts, the larger the pressing force (total pressing force) of an entire connecting apparatus becomes. For instance, in case where a 5 g pressing force is specified per contact, the total pressing force of the entire connecting apparatus with 20,000 contacts is approximately 100 kg. Also, when the pressing force acts on a probe base plate, the rim portion of the probe base plate is kept under restraint by a card holder, but the central portion may be free to move.
Therefore, according to the foregoing, the probe base plate may be largely bent such that the central portion is convex upward due to deflection of composing elements such as the wiring board and probe base plate when the tips of the contacts are pressed against the electrodes of the integrated circuit.
When the probe base plate bends as mentioned above, the height positions of the contacts (i.e., the probe tips) relative to the integrated circuits may become greatly different between the contacts located in the center of the probe base plate and the contacts located along the side of the rim of the probe base plate. This may cause a great difference in the amount of slide of the tips from tip to tip relative to the electrodes of the integrated circuit when the tips of the contacts are pressed against the electrodes of the integrated circuit.
In a connecting apparatus such as above, there may be contacts that cannot obtain a desired amount of slide, contacts whose tips are not sufficiently pressed against the electrode of the integrated circuits, and the like, when being tested. In such a case, it may be difficult or impossible to attach the connecting apparatus to the test apparatus and to confirm accurately a contact position, which may be marked by the distance of the scrape of the electrode by the contact, so that an accurate test may not be obtained.